1. Field of the Invention
This invention relates generally to an apparatus for separating a signal from a composite signal formed of two signals and, more particularly, to an apparatus for separating a chrominance signal from a composite video signal made up of a luminance signal and the chrominance signal, for use in a color television receiver or a video tape recorder.
2. Description of the Background
The provision of a composite color video signal ultimately requires the separation of its component signals at the time of display, or at the time of recording if they are to be recorded separately, and the systems to accomplish such separation known heretofore typically employ various kinds of filters to separate the luminance signal and the chrominance signal from the composite video. An example of such kinds of filtering is the so-called comb filter used in conjunction with a bandpass filter. It has also been proposed to use horizontal correlators in conjunction with these signal separating filters. These horizontal correlators involve the delaying of the composite signal to derive a number of signals and then comparing the relative amplitudes of various signals to a reference level signal to produce a correlated output.
A principal problem to date with the use of a bandpass filter as the luminance/chrominance separator is that a high-frequency cross-talk component of the luminance signal cannot be removed by such bandpass filter because it is of so high a frequency that it is in the filter passband required by the chrominance signal. This high-frequency luminance cross-talk is the so-called cross-color component. Thus, the use of the horizontal correlator has been required in order to provide optimum signal separation in addition to using conventional filtering.
Although the horizontal correlator approach does overcome some of the problems presented by using only filtering for signal separation, the delay lines employed in the horizontal correlator necessitate the loss of a portion of the chrominance signal at the time of separation. This signal loss occurs each time the chrominance signal is separated from the composite and if this horizontal correlator is used with video tape recorder equipment, in which the chrominance signal can be separated from the composite video a number of times in performance of a typical editing operation, the usable chrominance signal is reduced at each separation. Thus, the color information that is available is correspondingly diminished to an unacceptable level.